I am preparing LDH with co-precipitation method using aluminium chloride and calcium chloride. Upon addition of NaOH to AlCl3.6H2O and CaCl2.6H2O, not only LDH but also Al(OH)3 is formed. How should I prevent formation of this hydroxide?
Kautor, XRD confirms the formation of hydroxide.
thanks for your reply
Geetanjali Mishra , you say by increasing pH, but the coprepicitation made to constant pH
Hi Mishra, you are not the only one with these issues so do not feel too bad. We found similar things for Zn-Fe/Al Hydrotalcites. We managed to "get" the Fe based ( Article A new and improved synthesis method for the formation of ZnF...
)but not the Al-based yet, this is still a work in progress.
There is methods from papers you can try that likely you may have already seen
https://www.sciencedirect.com/science/article/pii/S1385894712016919
Article Synthesis and properties of CaAl-layered double hydroxides o...
but as you can see from our work on ZnFe LDHs, sometimes the literature is not always so helpful. Thus you can try to modify your method so as to avoid the Al(OH)3 impurities by making sure you work on a pH range (or another experimental variable such as starting salts) where the Al(OH)3 is dissolved or not formed.
Good luck
Hi Geetanjali Mishra
, could you please clarify if it is Al(III) replacement by Ca (II) or Ca (II) replaced with Al(III) by increasing the pH.Thank you
I think that the precipitation could done first with the bivalent metal due to the high concentration in the solution than the trivalent metal, then, the later could replace the bivalent in the formed sheet.
hi
it is all about the ratio of divalent and trivalent cations that you use
keep the ration between 2 to 1 and 4 to 1 this way you may prevent formation of aluminium hydroxide .
check the generic formula for LDH , the value for x must be between 0.2 to 0.33 in that formula ,which corresponds to the above mentioned ratio.
Dear Geetanjali Mishra,
in addition to other feed backs
-may you try adding all the three solid precursors simultaneously to your synthesis vessel keeping their ratio and dissolve and do all necessary adjustments
-keep vigorous string
Dear Maryam,
The following articles may be of help to you. Of course, the M+2/M+3 ratio is essential but pH is critical since it will determine the solubility of the M(OH)2 or M(OH)3 phases.
1- Robertson J. Geochemical characteristics of aluminum and magnesium secondary mineral phases in uranium mill tailings. Ph.D. University of Saskatchewan. 2017.
Article Mineralogical Controls on Aluminum and Magnesium in Uranium ...
Article Formation mechanism of layered double hydroxides in Mg2 +-, ...
Article A new and improved synthesis method for the formation of ZnF...
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